The present invention relates to an improved method of selectively controlling grassy weeds and broadleaf weeds in soybean crops.
2-Pyridyloxy(or thio)phenoxy alkanoate grass herbicides are well known herbicides and are described, for example, in Belgium Patent 868,875; PCT Application WP 7900094; EPO Application 483; U.S. Pat. No. 4,213,774; and French Pat. No. 7522436. These grass herbicides are useful for selectively controlling annual and perennial grassy weeds in the presence of desirable broadleaf crops.
Benzothiadiazinone derivatives, described in U.S. Pat. Nos. 4,015,130; 4,116,672; 4,155,746; 3,940,389; 3,708,277 and 3,621,017 are useful as herbicides and especially as broadleaf active herbicides.
Pyridyloxy(or thio)phenoxy alkanoate herbicides are typically applied post-emergently in the presence of nonionic surfactants. To extend the weed control spectrum in a given application, it has been taught that pyridyloxy(or thio)phenoxy alkanoate herbicides be mixed with benzothiadiazinone broadleaf active herbicides and thereafter applied to unwanted vegetation to provide a broad spectrum herbicidal composition effective against grasses and broadleaf weeds. See, for example, New Zealand Patent Specification 189,795 (published Nov. 19, 1981) which teaches combinations of pyridyloxyphenoxy derivatives and other herbicides.
In particular, New Zealand Patent Specification 189,795, teaches combining 2-(4-(2-pyridinyl)oxy)phenoxy propionate, n-butyl ester, i.e., commonly known as fluazifop-butyl and commercially available as FUSILADE.RTM. herbicide, with bentazon and applying the combination to soybeans for selective broad spectrum weed control. A serious problem associated with the combination of fluazifop-butyl and bentazon when applied to soybean crops is an increase in phytotoxicity to the soybean plants. This is an especially annoying problem in view of the fact that the herbicidal activity to grasses of pyridyloxyphenoxy alkanoate herbicides is decreased when combined with benzothiadiazinone derivatives. In fact, technical literature distributed by the manufacturer of FUSILADE.RTM. herbicide acknowledges the phytotoxicity of the combination of fluazifop-butyl and bentazon towards soybeans and specifically recommends avoidance of the combination being applied to soybean crops.
It has been found unexpectedly that pyridyloxy(or thio)phenoxy alkanoate grass herbicides that have a substituent other than hydrogen in the 3-position of the pyridine ring, when combined with benzothiadiazinone herbicides, exhibit less phytotoxicity or damage to soybean plants when the combination of herbicides is applied thereto, as compared to the combinations wherein the pyridyloxyphenoxy alkanoate herbicide contains hydrogen in the 3-position of the pyridine ring.